Bradyrhizobium sp. RD5-C2, isolated from soil that is not contaminated with 2,4-dichlorophenoxyacetic acid (2,4-D), degrades the herbicides 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). It possesses tfdAα and cadA (designated as cadA1), which encode 2,4-D dioxygenase and the oxygenase large subunit, respectively. In the present study, the genome of Bradyrhizobium sp. RD5-C2 was sequenced and a second cadA gene (designated as cadA2) was identified. The two cadA genes belonged to distinct clusters comprising the cadR1A1B1K1C1 and cadR2A2B2C2K2S genes. The proteins encoded by the cad1 cluster exhibited high amino acid sequence similarities to those of other 2,4-D degraders, while Cad2 proteins were more similar to those of non-2,4-D degraders. Both cad clusters were capable of degrading 2,4-D and 2,4,5-T when expressed in non-2,4-D-degrading Bradyrhizobium elkanii USDA94. To examine the contribution of each degradation gene cluster to the degradation activity of Bradyrhizobium sp. RD5-C2, cadA1, cadA2, and tfdAα deletion mutants were constructed. The cadA1 deletion resulted in a more significant decrease in the ability to degrade chlorophenoxy compounds than the cadA2 and tfdAα deletions, indicating that degradation activity was primarily governed by the cad1 cluster. The results of a quantitative reverse transcription-PCR analysis suggested that exposure to 2,4-D and 2,4,5-T markedly up-regulated cadA1 expression. Collectively, these results indicate that the cad1 cluster plays an important role in the degradation of Bradyrhizobium sp. RD5-C2 due to its high expression.

中文翻译：

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多基因簇及其在慢生根瘤菌中氯苯氧乙酸降解中的作用。 RD5-C2 从未受污染的土壤中分离出来。


慢生根瘤菌 sp. RD5-C2 是从未受 2,4-二氯苯氧基乙酸 (2,4-D) 污染的土壤中分离出来的，可降解除草剂 2,4-D 和 2,4,5-三氯苯氧基乙酸 (2,4,5- T）。它拥有 tfdAα 和 cadA（称为 cadA1），分别编码 2,4-D 双加氧酶和加氧酶大亚基。在本研究中，慢生根瘤菌的基因组。对 RD5-C2 进行测序并鉴定出第二个 cadA 基因（指定为 cadA2）。这两个 cadA 基因属于由 cadR1A1B1K1C1 和 cadR2A2B2C2K2S 基因组成的不同簇。 cad1簇编码的蛋白质与其他2,4-D降解剂的氨基酸序列具有高度相似性，而Cad2蛋白与非2,4-D降解剂的氨基酸序列更相似。当在非 2,4-D 降解慢生根瘤菌 USDA94 中表达时，两个 cad 簇都能够降解 2,4-D 和 2,4,5-T。研究每个降解基因簇对慢生根瘤菌降解活性的贡献。构建了 RD5-C2、cadA1、cadA2 和 tfdAα 缺失突变体。与 cadA2 和 tfdAα 删除相比，cadA1 删除导致降解氯苯氧基化合物的能力更显着下降，表明降解活性主要由 cad1 簇控制。定量逆转录 PCR 分析的结果表明，暴露于 2,4-D 和 2,4,5-T 会显着上调 cadA1 表达。总的来说，这些结果表明 cad1 簇在慢生根瘤菌的降解中发挥着重要作用。 RD5-C2 由于其高表达。